Ohwada Tomohiko, Kojima Daisuke, Kiwada Tatsuto, Futaki Shiroh, Sugiura Yukio, Yamaguchi Kentaro, Nishi Yoshinori, Kobayashi Yuji
Graduate School of Pharmaceutical Sciences, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
Chemistry. 2004 Feb 6;10(3):617-26. doi: 10.1002/chem.200305492.
A method was developed for synthesizing alpha,alpha-disubstituted glycine residues bearing a large (more than 15-membered) hydrophobic ring. The ring-closing metathesis reactions of the dialkenylated malonate precursors proceed efficiently, particularly when long methylene chains tether both terminal olefin groups. Surprisingly, the amino groups of these alpha,alpha-disubstituted glycines are inert to conventional protective reactions (e.g., N-tert-butoxycarbonyl (Boc) protection: Boc(2)O/4-dimethylaminopyridine (DMAP)/CH(2)Cl(2); N-benzyloxycarbonyl (Z) protection: Z-Cl/DMAP/CH(2)Cl(2)). Curtius rearrangement of the carboxylic acid functionality of the malonate derivative after ring-closing metathesis leads to formation of an amine functionality and can be catalyzed by diphenylphosphoryl azide. However, only the intermediate isocyanates can be isolated, even in the presence of alcohols such as benzyl alcohol. The isocyanates obtained by Curtius rearrangement in an aprotic solvent (benzene) were isolated in high yields and treated with 9-fluorenylmethanol in a high-boiling-point solvent (toluene) under reflux to give the N-9-fluorenylmethoxycarbonyl (Fmoc)-protected aminomalonate derivatives in high yield. These hydrophobic amino acids can be incorporated into a peptide by Fmoc solid-phase peptide synthesis and the acid fluoride activation method. The stability of the monomeric alpha-helical structure of a 17-amino-acid peptide was enhanced by replacement of two alanine residues with two hydrophobic amino acid residues bearing a cyclic 18-membered ring. The results of sedimentation equilibrium studies suggested that the peptide assembles into hexamers in the presence of 100 mM NaCl.
开发了一种合成带有大的（超过15元）疏水环的α,α-二取代甘氨酸残基的方法。二烯基化丙二酸酯前体的关环复分解反应高效进行，特别是当长亚甲基链连接两个末端烯烃基团时。令人惊讶的是，这些α,α-二取代甘氨酸的氨基对常规保护反应（例如，N-叔丁氧羰基（Boc）保护：Boc₂O/4-二甲氨基吡啶（DMAP）/CH₂Cl₂；N-苄氧羰基（Z）保护：Z-Cl/DMAP/CH₂Cl₂）呈惰性。关环复分解后丙二酸酯衍生物的羧酸官能团进行库尔提斯重排导致胺官能团的形成，并且可以由二苯基磷酰叠氮化物催化。然而，即使在存在苄醇等醇的情况下，也只能分离出中间异氰酸酯。在非质子溶剂（苯）中通过库尔提斯重排获得的异氰酸酯以高产率分离，并在高沸点溶剂（甲苯）中在回流下用9-芴甲醇处理，以高产率得到N-9-芴甲氧羰基（Fmoc）保护的氨基丙二酸酯衍生物。这些疏水氨基酸可以通过Fmoc固相肽合成和酰氟活化方法掺入肽中。通过用两个带有18元环的疏水氨基酸残基取代两个丙氨酸残基，增强了17个氨基酸肽的单体α-螺旋结构的稳定性。沉降平衡研究结果表明，在100 mM NaCl存在下，该肽组装成六聚体。
